India, Oct. 4 -- A new optical illusion is here, and it is a lot trickier than it looks. The image has a grid of 14 columns and 9 rows. The challenge is simple: spot the lone '400' hiding inside a grid packed with rows and rows of "404." Sounds easy enough, until your eyes start to blur and your brain gives up halfway through.

At first glance, every box in the image looks identical. A wall of 404 stretching across your screen. But hidden somewhere in that grid is one tiny cell that does not fit. One that quietly breaks the pattern.

The puzzle is designed to confuse your perception. The more you look, the more your brain tries to convince you that everything is the same. That is what makes it so frustrating and addictive.

Optical illusi...